It is known that graft polymers of methyl (meth)acrylate, styrene, acrylonitrile or the like grafted onto a butadiene-rich substrate, generally called MBS resins, are useful as reinforcement for enhancing the impact strength of vinyl chloride polymers or copolymers, generally termed PVC. However, such improvement is more often attainable at the expense of impairing the whiteness or the transparency of the obtained PVC moldings. Therefore, it is the object of the present invention to provide an MBS resin useful as a vinyl chloride polymer modifier capable of improving the impact resistance without impairing PVC's inherent whiteness and transparency.
Many types of modifiers have been employed in the prior art to achieve impact improvement in PVC. Typically, due to various reasons including the relative incompatibility of these modifiers and the differences in reflective index between the modifiers and the vinyl chloride polymers, most modifiers have failed to sustain good optical properties such as transparency, and, particularly, whiteness which are PVC's inherent advantages over other resins commonly used.
Whitworth et al, U.S. Pat. No. 3,264,373, disclose vinyl chloride compositions impact modified with a graft polymer of methyl(meth)acrylate on a butadiene/alkyl acrylate copolymer wherein the alkyl acrylate has a heat distortion temperature of less than 0.degree. C.
Graft polymer compositions comprising 10 to 70 percent by weight of a polymer or a copolymer of butadiene and grafts of firstly methyl(meth)acrylate and cross-linker, and secondly of styrene, and thirdly of methyl(meth)acrylate with an optional cross-linker, were blended to improve PVC's impact strength without crease whitening in U.K. Patent Specification No. 1,251,403.
Beer, U.S. Pat. No. 3,444,269, combined a vinyl halide graft copolymer of a vinyl halide monomer or copolymerizable monomer mixture and a chlorinated ethylene polymer with a methacrylate-butadiene-styrene (MBS)-type resin prepared by the one step polymerization of a mixture of styrene, methyl(meth)acrylate onto a butadiene-based rubbery copolymer wherein the ratio of styrene to methyl(meth)acrylate ranged from about 2:1 to about 1:2.
Idide et al, in U.S. Pat. Nos. 3,644,249 and 3,644,250, attempted to improve the transparency, impact strength, and/or surface gloss of polyvinyl chloride resin compositions by combining them with graft polymers in which either methyl(meth)acrylate and subsequently styrene, or styrene and subsequently methyl (meth)acrylate, were grafted to an elastomer of butadiene, n-butyl acrylate, and styrene in accordance with a ternary constitutional diagram.
Tanaka et al, U.S. Pat. No. 3,652,483, sought improve the impact properties without impairing other physical and chemical properties of vinyl chlorides by adding a graft copolymer of butadiene-styrene-methyl(meth)acrylate, co-precipitated with a polymethyl(meth)acrylate latex having a specific relative viscosity.
Mixtures of MBS-type resins with various refractive indexes have been used to improve the color transparency and the impact resistance of polyvinyl chloride resins by Tanaka et al, U.S. Pat. No. 3,657,390.
Tanaka, U.S. Pat. No. 3,842,144, discloses polyvinyl chlorides with impact modifiers obtained by the graft polymerization of two graft stages on a cross-linked butadiene/acrylate rubber latex in a sequential two stage process. There is no preference for the weight ratios of graft monomers.
Love, U.S. Pat. No. 3,922,320, has found that impact strength and processing characteristics are improved by the incorporation in polyvinyl chloride resins of an SAN resin and an MBS-type modifier prepared by grafting methyl(meth)acrylate and styrene onto polybutadiene in proportions of 15 to 30 percent of methyl(meth)acrylate units, 40 to 65 percent of butadiene units, and 10 to 40 percent of styrene units.
Polymers of butadiene and an alkyl acrylate grafted with an acrylic monomer, a styrene monomer, and an optional cross-linker and having an agglomerated particle size of 0.1 to 1 micron were prepared and were blended with polyvinyl chloride compositions by Chauvell et al, U.S. Pat. No. 4,078,018.
MBS-type resins have been rendered resistant to yellowing under mild oxidative conditions by the addition of 1,1,3-tris-(2-methyl-4-hydroxy-5-tert-butyl phenol) butane or the like in Clikemen et al, U.S. Pat. No. 4,379,876. Vinyl chloride polymers have been blended with these MBS-type resins as well.
Polyvinyl chlorides have also been blended with MBS-type resins that have been modified by the addition of a thermoplastic block elastomer which includes the residue of a monoalkenyl aromatic hydrocarbon and an alkadiene hydrocarbon which is normally incompatible with the vinyl halide polymer. The weight ratio of block elastomer to (meth)acrylate polymer ranges from about 1:5 to about 5:1. Wilschard, U.S. Pat. No. 4,423,188, reports that resultant molded articles are impact resistant and are substantially transparent and translucent.
Goldman, U.S. Pat. No. 4,443,585, prepares MBS-type resin compositions having a first stage of at least 70 percent butadiene and at least 10 percent C.sub.2 -C.sub.8 alkyl acrylate, a second stage of at least 80 percent styrene, and a third stage of at least 50 percent methyl(meth)acrylate and at least 1 percent C.sub.1 -C.sub.4 alkyl acrylate with a ratio of third stage to second stage of at least 1:1. These MBS-type resins are also blended with polyvinyl chloride resins.
Multi-stage produced high butadiene content MBS-type resins were found by Takaki et al, U.S. Pat. No. 4,508,876, to improve the impact resistance of vinyl chloride polymers without impairing their transparency.
Additionally, Hosoi et al, U.S. Pat. No. 4,624,987, disclose vinyl chloride polymer compositions reportedly capable of imparting solvent resistance, transparency and impact resistance to a molded article. These compositions include 5 to 50 percent of an MBS-type resin prepared by grafting a first stage predominantly of methyl(meth)acrylate and a second stage predominantly of styrene onto a butadiene/styrene rubber substrate wherein the first graft stage is 40 to 80 percent by weight of first and second graft stages combined and wherein the seed-polymerized SBR rubber has an average particle size of not less than 1500 angstroms.
Vinyl chloride resins have also been combined with various amounts of various MBS-type resins which are prepared by various methods as seen in U.S. Pat. Nos. 2,943,074; 3,287,443; 3,445,416; 3,651,177; 3,670,052; 3,772,409; 3,907,928; 4,041,106; and U.K. Patent Specification No. 1,299,400.
All of the above combinations and compositions suffer from one or more deficiencies not observed in the compositions of the present invention.